1. Field of the Invention
The invention relates to a nonaqueous electrolyte solution type lithium ion secondary battery system in which the degree of lithium deposition in a nonaqueous electrolyte solution type lithium ion secondary battery is determined. More particularly, the invention relates to a nonaqueous electrolyte solution type lithium ion secondary battery system that determines lithium deposition based on measured data without taking the target battery apart, a method for determining lithium deposition in that system, and a vehicle provided with that system.
2. Description of the Related Art
In nonaqueous electrolyte solution type lithium ion secondary batteries to be used in vehicles and elsewhere, deposition of metallic lithium (hereinafter also referred to as “lithium deposition”) may occur inside the battery as it is used. If a battery in such a state continues to be used as it is, it will adversely affect the original performance of the system. Therefore, it is necessary to ascertain the degree of lithium deposition in a nonaqueous electrolyte solution type lithium ion secondary battery.
Thus, Japanese Patent Application Publication No. 2009-63555 (JP-A-2009-63555) describes related art that attempts to determine whether there is lithium deposition. This technology calculates the power storage capacity of the battery in a running mode, and is then able to determine whether there is lithium deposition by comparing the calculated power storage capacity with the past power storage capacity. That is, when there is lithium deposition, the power storage capacity is lower than it is when there is no lithium deposition, so a determination as to whether there is lithium deposition is made by determining whether the power storage capacity has decreased.
However, aside from lithium deposition, age-related deterioration also results in a decrease in the power storage capacity. With the technology described in JP-A-2009-63555, it is difficult to clearly distinguish between these. Therefore, the determination accuracy of lithium deposition is comparatively low.